The invention relates to an infusion apparatus and to a control method for an infusion apparatus.
Specifically, though not exclusively, the invention can be usefully applied for infusion of a medical fluid to a patient, either directly into the patient's body, for example into his or her vascular system, or via an extracorporeal blood circuit connected to the patient.
WO 87/05225 teaches an infusion system comprising a drip chamber having a pointed upper inlet end for insertion of a container of an infusion fluid. The chamber is provided with an inlet valve and an outlet valve controlled by a control unit. The top of the chamber is connected to a piston gas compressor via an auxiliary line provided with a pressure sensor. The control of the infusion flow rate is done as follows. With both the valves closed and an initial pressure P1 in the chamber, the piston is displaced forward such as to reduce the volume by a predetermined quantity ΔV. According to Boyle's law, this reduction in volume corresponds to a proportional increase in gas pressure ΔP. At this point the outlet valve is opened to dispense the infusion fluid. When the pressure has dropped by a quantity ΔP, which means that an infusion fluid volume of ΔV has been dispensed, the outlet valve is closed. After this the piston returns back to its initial position, the inlet valve is opened so the chamber can be filled to initial pressure P1, and a new cycle commences.
EP 1319417 illustrates a disposable infusion system for injecting an infusion fluid into the body of a patient. The infusion system comprises a fluid conduit situated between a source of an infusion fluid and the patient, a peristaltic pump operating on the fluid conduit, a gas-liquid separation chamber downstream of the pump, a pressure sensor in the chamber, and a clamp for blocking the fluid conduit downstream of the chamber. The pressure sensor is arranged on a service line which branches from the top of the chamber and which is provided with a hydrophobic-membrane protection device for protecting the pressure sensor against contamination by the liquid in the chamber. If the liquid reaches the membrane the membrane becomes gas-sealed and is no longer able to transmit the pressure to the sensor. In these conditions the measured pressure does not correspond to the real pressure in the chamber. A monitoring unit determines the quantity of gas in the system so as to detect, over time, a situation of risk of the liquid reaching the membrane. The monitoring unit measures the initial pressure P1, and then injects into or extracts from the system a predetermined fluid volume ΔV, after which it newly measures the pressure P2, and calculates the gas volume in the system as a function of P2, P1 and ΔV.
EP 1319417 teaches a further monitoring method of a disposable fluid conduit system connected to a medical apparatus, in particular with the aim of testing the integrity of the system (for example the absence of leaks) and of checking that the installed disposable system is the appropriate one for the desired treatment. The monitoring method includes continuously measuring the pressure in the system, injecting or extracting a volume of fluid ΔV into or from the system until a predetermined pressure P2 is reached in the system, and finally determining the state of the system from a comparison between ΔV and a standard predetermined value.